(VB.NET) Sign PDF: Choosing RSASSA-PSS or PKCS1-v1_5 and Hash Algorithm

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This example demonstrates how to choose between RSASSA-PSS vs. PKCS1-v1_5 and the hash algorithm when signing a PDF.

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' This example requires the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.

Dim pdf As New Chilkat.Pdf

' Load a PDF to be signed.
' The "hello.pdf" is available at https://chilkatsoft.com/hello.pdf
Dim success As Boolean = pdf.LoadFile("qa_data/pdf/hello.pdf")
If (success = False) Then
    Debug.WriteLine(pdf.LastErrorText)
    Exit Sub
End If



' Options for signing are specified in JSON.
Dim json As New Chilkat.JsonObject

' In most cases, the signingCertificateV2 attribute is needed.
json.UpdateInt("signingCertificateV2",1)

' ---------------------------------------------------------------------------------------------------------------------------
' This example is the same as the example at Sign a PDF (Simplest Example Possible)
' but with the following lines added to specify the signature scheme and hash algorithm.

' The signature schemes PKCS-v1_5 and RSASSA-PSS have differences. 
' PKCSV1_5 is deterministic. The same message and key will produce an identical signature value each time. 
' PSS is randomized and will produce a different signature value each time.

' To choose the hash algorithm:
' (The typical choices are sha1, sha256, sha384, and sha512.)
json.UpdateString("hashAlgorithm","sha256")

' To choose PKCSV1_5:
json.UpdateString("signingAlgorithm","pkcs")
' Alternatively, to choose RSASSA-PSS:
json.UpdateString("signingAlgorithm","pss")

' If not specified, the default is SHA256 with PKCS-v1_5.

' The remainder of this example is the same as the example at Sign a PDF (Simplest Example Possible)
' ---------------------------------------------------------------------------------------------------------------------------

' Put the signature on page 1, top left
json.UpdateInt("page",1)
json.UpdateString("appearance.y","top")
json.UpdateString("appearance.x","left")

' Use a font scale of 10.0
json.UpdateString("appearance.fontScale","10.0")

' In this example, the appearance of the digital signature will contain three lines:
' 1) The signing certificate's common name
' 2) The current date/time
' 3) Some arbitrary text.
' The keyword "cert_cn" is replaced with the Certificate's Subject Common Name.
' The keyword "current_dt" is replaced with the current date/time.
' Any number of appearance text lines can be added.
json.UpdateString("appearance.text[0]","Digitally signed by: cert_cn")
json.UpdateString("appearance.text[1]","current_dt")
json.UpdateString("appearance.text[2]","The crazy brown fox jumps over the lazy dog.")

' Load the signing certificate. (Use your own certificate.)
Dim cert As New Chilkat.Cert
success = cert.LoadPfxFile("qa_data/pfx/myPdfSigningCert.pfx","secret")
If (success = False) Then
    Debug.WriteLine(cert.LastErrorText)
    Exit Sub
End If


' Tell the pdf object to use the certificate for signing.
success = pdf.SetSigningCert(cert)
If (success = False) Then
    Debug.WriteLine(pdf.LastErrorText)
    Exit Sub
End If


success = pdf.SignPdf(json,"qa_output/hello_signed.pdf")
If (success = False) Then
    Debug.WriteLine(pdf.LastErrorText)
    Exit Sub
End If


Debug.WriteLine("The PDF has been successfully cryptographically signed.")

' The appearance of the signature appears in Adobe Acrobat as shown here: